Measurement of elastic force on a scanned probe near a solid surface

The physical nature of the forces acting between a laterally vibrating probe in air near a solid surface has been investigated using a calibrated method for the experimental determination of dynamic force. The frequency response of the probe vibrating near its fundamental bending resonance was measured as a function of distance as the probe approached the surface. The experimental results were compared with a continuum-mechanical model of bending waves in a rod; the nature of the forces was inferred by determining the effect of various boundary conditions on the standing-wave motion of the probe. The results conclusively show that while in the initial stage of approach the force is dominated by fluid-dynamic effects, in the final stage of approach an elastic force appears. The appearance of the elastic deformation is characterized by a shift in the resonant frequency of the vibrating probe. (C) 1996 American Institute of Physics.